When testing the trailer service brakes, what should you do first?

When testing the trailer service brakes, the first step should be to release the parking brake and roll forward slowly. This is important because it allows the brakes to engage and provides an opportunity to assess their functionality under actual driving conditions. By rolling forward slowly, you can safely observe how the brakes respond without putting yourself or others at risk.

Releasing the parking brake is crucial as it ensures that the trailer is free to move, enabling the testing of the service brakes specifically. This approach not only checks the effectiveness of the braking system but also helps identify any potential issues with the brakes functioning correctly while the vehicle is in motion.

Engaging the parking brake fully would prevent movement and not contribute to testing the service brakes. Checking the brake fluid levels is essential for overall brake system maintenance but does not directly relate to testing the brakes themselves. Driving to a safe area before testing may be a good practice in some contexts, but the actual test of the service brakes requires rolling forward to assess their performance.